WO2024065386A1

WO2024065386A1 - Electrochemical device and electronic device

Info

Publication number: WO2024065386A1
Application number: PCT/CN2022/122550
Authority: WO
Inventors: 孙振贺; 付红岩
Original assignee: 宁德新能源科技有限公司
Priority date: 2022-09-29
Filing date: 2022-09-29
Publication date: 2024-04-04
Also published as: CN116325266A

Abstract

An electrochemical device and an electronic device. By providing an inactive material layer (50) on a second surface (10b) of a single-sided area (30) of a positive electrode current collector (10) while matching with an electrolyte, the risk of a positive electrode piece (100) experiencing an abnormality after the electrochemical device undergoes charge and discharge cycles is reduced, and the risk of lithium precipitation on a negative electrode piece (200) is reduced, thereby reducing the risk of failure of the electrochemical device during the charge and discharge cycles.

Description

Electrochemical device and electronic device

Technical Field

The present application relates to the field of electrochemical technology, and in particular to an electrochemical device and an electronic device.

Background technique

Most of the electrode assemblies in existing secondary batteries (such as lithium-ion batteries) have exposed positive current collectors (usually aluminum foil), for example, a winding structure with a positive current collector at the end, a winding structure with a die-cut aluminum tab, or a stacked structure with a positive single-sided area at the end. As the voltage system of lithium-ion batteries continues to increase, the oxidation ability of the positive electrode sheet to the electrolyte is also continuously enhanced when fully charged. In order to reduce the oxidation of the electrolyte by the positive electrode sheet, the existing technology usually increases the content of fluorine-containing compounds in the electrolyte to improve the protection of the positive and negative electrode sheets under high voltage.

However, fluorine-containing compounds, such as fluorine-containing additives and fluorine-containing lithium salts, are prone to undergo a defluorination reaction under the action of Lewis acids (such as PF ₅ ) generated by the decomposition of the electrolyte to produce HF. In this case, after the lithium-ion battery is injected, the electrolyte contacts the exposed positive electrode current collector, and the HF in the electrolyte and the positive electrode current collector react to generate impurities. The generated impurities will diffuse with the electrolyte inside the lithium-ion battery and gather in a specific area of the positive electrode sheet (for example, the edge of the positive electrode material layer set in the single-sided area of the positive electrode current collector), causing abnormalities in the positive electrode sheet, which will affect the lithium deposition of the negative electrode sheet, thereby causing the lithium-ion battery to fail during the charge and discharge cycle. Based on this, how to reduce the risk of failure of lithium-ion batteries during the charge and discharge cycle has become a technical problem that needs to be solved urgently by those skilled in the art.

Summary of the invention

The purpose of the present application is to provide an electrochemical device and an electronic device to reduce the risk of failure of the electrochemical device during the charge and discharge cycle.

It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

In a first aspect, the present application provides an electrochemical device, which includes an electrode assembly, an electrolyte, and a packaging bag for containing the electrode assembly and the electrolyte. The electrolyte includes a fluorine-containing compound. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is arranged between the positive electrode sheet and the negative electrode sheet. The electrode assembly is stacked by the positive electrode sheet, the separator, and the negative electrode sheet. The positive electrode sheet includes a positive current collector, a positive active material layer, and an inactive material layer. The positive current collector is an aluminum foil and includes silicon element. The mass percentage of silicon element in the positive current collector is a%, 0.03≤a≤0.13; the positive current collector includes a first surface and a second surface opposite to each other. The positive current collector has a single-sided area, the single-sided area includes a first part, the second surface of the first part is located on the outer surface of the electrode assembly, the first surface of the single-sided area is provided with a positive active material layer, and the second surface of the single-sided area is provided with an inactive material layer; the inactive material layer includes an inactive material, and the inactive material includes at least one of an inorganic oxide or a non-metallic element. By selecting the positive electrode current collector provided by the present application, and setting an inactive material layer on the second surface of the single-sided area of the positive electrode current collector, and at the same time using the electrolyte of the present application, after the electrochemical device is charged and discharged, the risk of abnormalities in the positive electrode plate is reduced, and the risk of lithium deposition in the negative electrode plate is reduced, thereby reducing the risk of failure of the electrochemical device during the charge and discharge cycle.

In some embodiments of the present application, the inactive material layer covers the second surface of the single-sided area. It is understandable that the entire area of the second surface of the single-sided area is provided with an inactive material layer. In this way, the inactive material layer acts as an inert layer between the electrolyte and the positive electrode current collector, completely isolating the electrolyte from the positive electrode current collector, further reducing the possibility of contact between the electrolyte and the positive electrode current collector, and further reducing the content of by-products produced by the reaction between the electrolyte and the positive electrode current collector. As a result, the risk of by-products accumulating in specific areas or other areas of the positive electrode sheet. After the electrochemical device is charged and discharged, the risk of abnormalities in the positive electrode sheet is reduced, and the risk of lithium precipitation in the negative electrode sheet is reduced, thereby reducing the risk of failure of the electrochemical device during the charge and discharge cycle.

In some embodiments of the present application, the inorganic oxide includes at least one of aluminum oxide, silicon oxide, calcium oxide, boehmite or calcium carbonate. The non-metallic element includes at least one of silicon, carbon or boron. By selecting the above-mentioned inorganic oxides and non-metallic elements, the risk of abnormality of the positive electrode sheet is reduced, and the risk of lithium deposition of the negative electrode sheet is reduced, thereby reducing the risk of failure of the electrochemical device during the charge and discharge cycle.

In some embodiments of the present application, the Dv50 of the inorganic oxide is 0.1 μm to 30 μm, and the Dv50 of the non-metallic element is 0.1 μm to 10 μm. Regulating the average particle size Dv50 of the inorganic oxide and the non-metallic element within the above range is more conducive to regulating the thickness of the inactive material layer within a suitable range, reducing the risk of abnormalities in the positive electrode sheet, and reducing the risk of lithium deposition in the negative electrode sheet, thereby reducing the risk of failure of the electrochemical device during the charge and discharge cycle.

In some embodiments of the present application, the inactive material layer also includes an inactive material layer binder, and the inactive material layer binder includes at least one of polytetrafluoroethylene, chloroprene rubber, nitrile rubber, styrene-butadiene rubber, styrene-butadiene rubber, carboxyl rubber, chlorosulfonated polyethylene rubber, phenolic resin, epoxy resin or silicone resin. The mass ratio of the inactive material and the inactive material layer binder is (70-98): (2-30). By selecting the above-mentioned binder and regulating the mass ratio of the inactive material in the inactive material layer and the inactive material layer binder within the above-mentioned range, the risk of abnormality of the positive electrode sheet is reduced, and the risk of lithium precipitation of the negative electrode sheet is reduced, thereby reducing the risk of failure of the electrochemical device during the charge and discharge cycle.

In some embodiments of the present application, the fluorine-containing compound includes a fluorine-containing additive, and the mass percentage of the fluorine-containing additive in the electrolyte is c%, 0.1≤c≤40. The electrolyte includes the fluorine-containing additive, and the mass percentage of the fluorine-containing additive in the electrolyte is regulated within the above range, so that the risk of abnormality of the positive electrode sheet is reduced, thereby reducing the risk of failure of the electrochemical device during the charge and discharge cycle.

In some embodiments of the present application, the thickness of the inactive material layer is b μm, 3 ≤ b ≤ 20. By adjusting the thickness of the inactive material layer within the above range, the risk of abnormality of the positive electrode sheet is reduced, and the risk of lithium deposition of the negative electrode sheet is reduced, thereby reducing the risk of failure of the electrochemical device during the charge and discharge cycle.

In some embodiments of the present application, 3≤b≤10. The inactive material layer can have a more suitable thickness, meet the demand of reducing the risk of failure of the electrochemical device during the charge and discharge cycle, and reduce the influence of the inactive material layer on the energy density of the electrochemical device. At the same time, in the rolling process after the electrode sheet is coated, the rolling device acts on the inactive material layer, reducing the risk of the rolling device directly transitioning from the positive electrode active material layer to the positive electrode current collector, thereby causing the positive electrode segment to break.

In some embodiments of the present application, 0.003≤a/b≤0.025. By regulating the value of a/b within the above range, the mass percentage of silicon in the positive electrode current collector and the thickness of the inactive material layer act synergistically, which is more conducive to reducing the risk of failure of the electrochemical device during the charge and discharge cycle. In some embodiments of the present application, 0.003≤a/b≤0.02. The risk of failure of the electrochemical device during the charge and discharge cycle can be further reduced.

In some embodiments of the present application, 0.1≤c/b≤13. By adjusting the value of c/b within the above range, the mass percentage of the fluorine-containing additive in the electrolyte and the thickness of the inactive material layer have a synergistic effect, which is more conducive to reducing the risk of failure of the electrochemical device during the charge and discharge cycle. In some embodiments of the present application, 0.1≤c/b≤6.7. The risk of failure of the electrochemical device during the charge and discharge cycle can be further reduced.

In some embodiments of the present application, the fluorine-containing additive includes at least one of fluoroethylene carbonate, bis(fluoromethyl)ethylene carbonate, bis(difluoromethyl)ethylene carbonate, bis(trifluoromethyl)ethylene carbonate, bis(2-fluoroethyl)ethylene carbonate, bis(2,2-difluoroethyl)ethylene carbonate, bis(2,2,2-trifluoroethyl)ethylene carbonate, 2-fluoroethyl methylethylene carbonate, 2,2-difluoroethyl methylethylene carbonate or 2,2,2-trifluoroethyl methylethylene carbonate. The use of the above-mentioned types of fluorine-containing additives is more conducive to reducing the oxidation ability of the positive electrode sheet to the electrolyte, forming a uniform and dense protective film on the surface of the positive electrode sheet and the negative electrode sheet to protect the positive electrode sheet and the negative electrode sheet.

In some embodiments of the present application, the fluorine-containing substance includes a fluorine-containing lithium salt, and the fluorine-containing lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(trifluoromethane)sulfonyl imide, lithium bis(fluorosulfonyl imide), lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium perfluorobutylsulfonate, lithium bis(sulfonyl imide) or lithium fluoride. The addition of the fluorine-containing lithium salt is more conducive to providing high ionic conductivity and making the transmission rate of lithium ions faster.

In some embodiments of the present application, the structure of the electrode assembly is a stacked structure; alternatively, the electrode assembly is a wound structure, and the positive electrode current collector further includes a double-sided region, and along the winding direction, the double-sided region is sequentially connected to the single-sided region.

The second aspect of the present application provides an electronic device, which includes the electrochemical device provided in the first aspect of the present application. Therefore, the beneficial effects of the electrochemical device provided in the first aspect of the present application can be obtained.

Of course, implementing any product or method of the present application does not necessarily require achieving all of the advantages described above at the same time.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present application and the technical solutions of the prior art, the following briefly introduces the drawings required for use in the embodiments and the prior art. Obviously, the drawings described below are only some embodiments of the present application, and a person of ordinary skill in the art can also obtain other drawings based on these drawings.

FIG1 is a schematic diagram of the structure of an electrode assembly in some embodiments of the present application;

FIG2 is a schematic diagram of the cross-sectional structure of the positive electrode sheet in the electrode assembly of FIG1 along its thickness direction in an unfolded state;

FIG3 is a schematic structural diagram of the positive electrode sheet of FIG2 observed along its thickness direction;

FIG4 is a schematic diagram of the structure of an electrode assembly in some embodiments of the present application;

FIG5 is a schematic diagram of the cross-sectional structure of the positive electrode sheet in the electrode assembly of FIG4 in an unfolded state along its thickness direction;

FIG6 is a schematic diagram of the structure of a positive electrode sheet in some embodiments of the present application;

FIG. 7 is a schematic diagram of the cross-sectional structure of the positive electrode sheet of Comparative Example 1 along its thickness direction in an unfolded state.

Detailed ways

In order to make the purpose, technical solution, and advantages of the present application more clearly understood, the present application is further described in detail with reference to the accompanying drawings and examples. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field belong to the scope of protection of the present application.

It should be noted that in the specific embodiments of the present application, a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to a lithium-ion battery.

The electrode assembly in an electrochemical device (such as a lithium-ion battery) will generally have an exposed positive electrode current collector. The positive electrode current collector in the prior art is usually made of aluminum foil with a silicon mass percentage of 0.06% to 0.18%, and most of the silicon is in the form of silicon dioxide or silicate. As the voltage system of the electrochemical device continues to increase, the oxidation ability of the positive electrode plate to the electrolyte is also continuously enhanced when fully charged. In order to reduce the oxidation of the electrolyte by the positive electrode plate, the prior art often increases the content of fluorine-containing compounds in the electrolyte to improve the protection of the positive and negative electrode plates under high voltage.

However, fluorine-containing compounds, such as fluorine-containing additives and fluorine-containing lithium salts, are prone to undergo a defluorination reaction under the action of Lewis acids (such as PF ₅ ) generated by the decomposition of the electrolyte to produce HF. In this case, after the electrochemical device is injected, the electrolyte contacts the exposed aluminum foil, and the HF in the electrolyte may react with components in the aluminum foil, such as silicon dioxide or silicate, to generate byproduct fluorine silicon compounds. The byproduct fluorine silicon compounds diffuse inside the electrochemical device and gather in a specific area of the positive electrode plate (for example, the edge position of the positive electrode active material layer set in the single-sided area of the positive electrode collector), causing the positive electrode plate to become abnormal (such as obvious color difference in the local area, increased silicon content), and the abnormal area of the positive electrode plate cannot be delithiated normally. Lithium ions are released from the edge of the abnormal area of the positive electrode plate, which will cause the negative electrode plate corresponding to the edge of the abnormal area to have insufficient lithium insertion positions, resulting in lithium precipitation, thereby causing the electrochemical device to fail during the charge and discharge cycle. In order to solve the problem of failure of the electrochemical device during the charge and discharge cycle, the present application provides an electrochemical device and an electronic device.

The first aspect of the present application provides an electrochemical device, which includes an electrode assembly, an electrolyte, and a packaging bag for containing the electrode assembly and the electrolyte, wherein the electrolyte includes a fluorine-containing compound, the electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet, and the electrode assembly is stacked by the positive electrode sheet, the separator, and the negative electrode sheet. The positive electrode sheet includes a positive current collector, a positive active material layer, and an inactive material layer, the positive current collector is aluminum foil and includes silicon element, and the mass percentage of silicon element in the positive current collector is a%, 0.03≤a≤0.13; the positive current collector includes a first surface and a second surface opposite to each other. The positive current collector includes aluminum element and silicon element, and the mass percentage of silicon element in the positive current collector is a%, 0.03≤a≤0.13. The positive electrode current collector has a single-sided area, which is located at the end of the positive electrode current collector along its own length direction, and includes a first part, the second surface of the first part is located on the outer surface of the electrode assembly, the first surface of the single-sided area is provided with a positive electrode active material layer, and the second surface of the single-sided area is provided with an inactive material layer; the inactive material layer includes an inactive material, and the inactive material includes at least one of an inorganic oxide or a non-metallic element. The length direction of the positive electrode current collector is along the winding direction of the wound electrode assembly.

It can be understood that the single-sided area is a section of the positive electrode current collector, therefore, the first surface of the single-sided area is the first surface of the positive electrode current collector, and the second surface of the single-sided area is the second surface of the positive electrode current collector. The first part is a section or the entirety of the single-sided area, that is, it is also a section of the positive electrode current collector, therefore, the first surface of the first part is the first surface of the positive electrode current collector, and the second surface of the first part is the second surface of the positive electrode current collector.

For example, the value of a is 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13 or any value between any two of the above numerical ranges. When the mass percentage of silicon in the positive electrode current collector is too small, that is, when the value of a is less than 0.03, the strength of the aluminum foil is insufficient, the wear resistance is poor, and the risk of cold-pressing and breaking the positive electrode sheet is prone to occur during the preparation of the positive electrode sheet; when the mass percentage of silicon in the positive electrode current collector is too large, that is, when the value of m is greater than 0.13, the strength of the positive electrode current collector is too large, resulting in poor ductility, and the risk of the positive electrode current collector being broken is prone to occur during the subsequent winding process (such as winding of the positive electrode current collector, winding of the positive electrode sheet, winding during the preparation of the electrode assembly, etc.); at the same time, the conductivity of the positive electrode current collector is deteriorated. By regulating the mass percentage of silicon in the positive electrode current collector within the above range, the manufacturing abnormalities of the positive electrode current collector can be reduced, so that the strength and toughness of the positive electrode current collector meet the requirements of its preparation process and have good conductivity.

The single-sided area includes a first part, and the second surface of the first part is located on the outer surface of the electrode assembly. An inactive material layer is arranged on the second surface of the single-sided area, so that the inactive material layer serves as an inert layer between the electrolyte and the positive electrode current collector, physically isolates the electrolyte, and reduces the possibility of the electrolyte reacting with the positive electrode current collector to produce by-products, so as to reduce the content of the by-products and reduce the risk of by-products gathering in specific areas or other areas of the positive electrode sheet.

In general, by selecting the positive electrode current collector provided by the present application, setting an inactive material layer on the second surface of the single-sided area of the positive electrode current collector, and simultaneously using the electrolyte of the present application, the risk of abnormalities occurring in the positive electrode plate and the risk of lithium deposition occurring in the negative electrode plate of the electrochemical device after charge and discharge cycles is reduced, thereby reducing the risk of failure of the electrochemical device during the charge and discharge cycle.

The present application does not particularly limit the type of aluminum foil, and it can be any aluminum foil known in the art, as long as it can achieve the purpose of the present application.

The present application has no particular restrictions on the method for controlling the mass percentage of silicon in the positive electrode current collector, as long as the purpose of the present application can be achieved, for example, by adjusting the ratio of the components in the positive electrode current collector and the types of the components.

Exemplarily, in some embodiments of the present application, as shown in FIGS. 1 to 5 , the structure of the electrode assembly 001 is a winding structure, the winding direction is indicated by W, the electrode assembly 001 includes a positive electrode sheet 100, a negative electrode sheet 200, and a separator 300 disposed between the positive electrode sheet 100 and the negative electrode sheet 200, the positive electrode sheet 100 includes a positive current collector 10, a positive electrode active material layer 20, and an inactive material layer 50. The positive current collector 10 includes a first surface 10a and a second surface 10b opposite to each other, the positive current collector 10 includes a single-sided area 30, the first surface 10a of the single-sided area 30 is provided with the positive electrode active material layer 20, and the second surface 10b of the single-sided area 30 is provided with the inactive material layer 50. The single-sided area 30 includes a first portion 301, and the second surface 10b of the first portion 301 is located on the outer surface of the electrode assembly 001. As shown in FIGS. 1 to 3 , the positive electrode current collector 10 further includes a double-sided region 40, a first double-sided empty foil region 61, and a second double-sided empty foil region 62. The portion of the single-sided region 30 other than the first portion 301 is not located on the outer surface of the electrode assembly 001, and the second surface 10b of the first portion 301 is located on the outer surface of the electrode assembly 001. The positive electrode current collector in the electrode assembly shown in FIG4 does not include the second double-sided empty foil region 62, and includes the double-sided region 40, the single-sided region 30, and the first double-sided empty foil region 61. As shown in FIGS. 4 and 5 , the first portion 301 can be understood as the single-sided region 30, and the second surface 10b of the first portion 301 can also be understood as the second surface 10b of the single-sided region 30, that is, the second surface 10b of the single-sided region 30 is located on the outer surface of the electrode assembly 001.

For example, in some embodiments of the present application, the structure of the electrode assembly is a laminate structure, and the electrode assembly is stacked by a positive electrode sheet, a negative electrode sheet, and a separator located between the positive electrode sheet and the negative electrode sheet. The two outermost sides of the electrode assembly along the thickness direction are both single-sided positive electrode sheets. Specifically, as shown in FIG6 , the single-sided positive electrode sheet includes a positive electrode collector 10, and the positive electrode collector 10 includes a first surface 10a and a second surface 10b opposite to each other. The positive electrode collector 10 includes a single-sided area 30, and the first surface 10a of the single-sided area 30 is provided with a positive electrode active material layer 20, and the second surface 10b of the single-sided area 30 is provided with an inactive material layer 50. The single-sided area 30 includes a first portion 301, and the second surface 10b of the first portion 301 is located on the outer surface of the electrode assembly 001. Among them, the first portion 301 can be understood as the single-sided area 30, and the second surface 10b of the first portion 301 can also be understood as the second surface 10b of the single-sided area 30, that is, the second surface 10b of the single-sided area 30 is located on the outer surface of the electrode assembly. Typically, the positive electrode sheet that is not located on the outer surface of the electrode assembly is a double-sided positive electrode sheet, which includes a positive electrode collector. The positive electrode collector includes a first surface and a second surface opposite to each other, and positive electrode active material layers are disposed on the first surface and the second surface.

In some embodiments of the present application, the inorganic oxide includes at least one of aluminum oxide, silicon oxide, calcium oxide, boehmite or calcium carbonate, and the non-metallic element includes at least one of silicon, carbon or boron. The selection of the above-mentioned types of inorganic oxides and non-metallic elements is more conducive to the inertness of the inactive material layer, and the electrolyte is physically isolated from the positive electrode current collector to reduce the possibility of the electrolyte reacting with the positive electrode current collector to produce by-products, and reduce the content of by-products. In this way, the risk of by-products accumulating in specific areas or other areas of the positive electrode sheet is reduced. As a result, after the electrochemical device is charged and discharged, the risk of abnormalities in the positive electrode sheet is reduced, and the risk of lithium precipitation in the negative electrode sheet is reduced, thereby reducing the risk of failure of the electrochemical device during the charge and discharge cycle.

In the present application, there is no particular restriction on the form in which the non-metallic element is added to the inactive material layer, as long as the purpose of the present application can be achieved. For example, silicon is added in the form of silicon powder, carbon is added in the form of conductive carbon, and boron is added in the form of elemental boron powder.

In some embodiments of the present application, the Dv50 of the inorganic oxide is 0.1 μm to 30 μm, and the Dv50 of the non-metallic element is 0.1 μm to 10 μm. For example, the Dv50 of the inorganic oxide is 0.1 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or any value between any two of the above numerical ranges. The Dv50 of the non-metallic element is 0.1 μm, 1 μm, 5 μm, 10 μm, or any value between any two of the above numerical ranges. Regulating the average particle size Dv50 of the inorganic oxide and the non-metallic element within the above range is more conducive to regulating the thickness of the inactive material layer within a suitable range, so that the inactive material layer physically isolates the electrolyte from the positive electrode current collector to reduce the possibility of the electrolyte reacting with the positive electrode current collector to produce by-products and reduce the content of by-products. In this way, the risk of by-products accumulating in specific areas or other areas of the positive electrode sheet is reduced. As a result, after the electrochemical device has been charged and discharged for a cycle, the risk of abnormalities occurring in the positive electrode plate is reduced, and the risk of lithium deposition occurring in the negative electrode plate is reduced, thereby reducing the risk of failure of the electrochemical device during the charge and discharge cycle.

In the present application, Dv50 means a particle size at which the volume accumulation is 50% from the smaller particle size side in the volume-based particle size distribution of the inorganic oxide or the non-metallic simple substance.

In some embodiments of the present application, the inactive material layer also includes an inactive material layer binder, and the inactive material layer binder includes at least one of polytetrafluoroethylene, chloroprene rubber, nitrile rubber, styrene-butadiene rubber, styrene-butadiene rubber, carboxyl rubber, chlorosulfonated polyethylene rubber, phenolic resin, epoxy resin or silicone resin. The mass ratio of the inactive material and the inactive material layer binder is (70-98): (2-30). For example, the mass ratio of the inactive material and the binder is 70:30, 75:25, 80:20, 85:15, 90:10, 95:5, 98:2 or any value between any two of the above numerical ranges. Selecting the above-mentioned inactive material layer binder and regulating the mass ratio of the inactive material and the inactive material layer binder in the inactive material layer within the above range is more conducive to preparing an inactive material layer with good isolation effect, physically isolating the electrolyte from the positive electrode current collector, further reducing the possibility of contact between the electrolyte and the positive electrode current collector, and further reducing the content of by-products produced by the reaction between the electrolyte and the positive electrode current collector. As a result, the risk of byproducts accumulating in specific areas or other areas of the positive electrode sheet is reduced. After the electrochemical device undergoes charge and discharge cycles, the risk of abnormalities in the positive electrode sheet is reduced, and the risk of lithium deposition in the negative electrode sheet is reduced, thereby reducing the risk of failure of the electrochemical device during the charge and discharge cycle.

In some embodiments of the present application, the fluorine-containing compound includes a fluorine-containing additive, and the mass percentage of the fluorine-containing additive in the electrolyte is c%, 0.1≤c≤40. For example, the value of c is 0.1, 2.0, 5.0, 10.0, 15.0, 20.0, 25.0, 30.0, 35.0, 40.0 or any value between any two of the above numerical ranges. The electrolyte includes a fluorine-containing additive, and the mass percentage of the fluorine-containing additive in the electrolyte is regulated within the above range, which can enhance the electrolyte's ability to protect the negative electrode sheet, form a uniform and dense protective film on the surface of the negative electrode sheet, and thus improve the cycle performance of the electrochemical device; at the same time, reduce the content of the byproduct fluorine silicon compound generated by the reaction of HF in the electrolyte with the silicon element in the positive electrode collector. In this way, the risk of abnormality of the positive electrode sheet is reduced, thereby reducing the risk of failure of the electrochemical device during the charge and discharge cycle.

In some embodiments of the present application, the thickness of the inactive material layer is bμm, 3≤b≤20. For example, the value of b is 3, 4, 6, 8, 10, 12, 14, 16, 18, 20 or any value between any two of the above numerical ranges. The thickness of the inactive material layer is regulated within the above range, without increasing the volume of the electrochemical device and affecting the energy density of the electrochemical device, which is more conducive to the inactive material layer as an inert layer between the electrolyte and the positive electrode collector, isolating the electrolyte from the positive electrode collector, reducing the possibility of contact between the electrolyte and the positive electrode collector, and reducing the content of byproducts produced by the reaction between the electrolyte and the positive electrode collector. As a result, the risk of byproducts accumulating in specific areas or other areas of the positive electrode sheet. After the electrochemical device is charged and discharged for cycling, the risk of abnormality of the positive electrode sheet is reduced, and the risk of lithium precipitation of the negative electrode sheet is reduced, thereby reducing the risk of failure of the electrochemical device during the charge and discharge cycle. In some embodiments of the present application, 3≤b≤10. The inactive material layer can have a more suitable thickness to meet the demand for reducing the risk of failure of the electrochemical device during the charge and discharge cycle, and can also reduce the impact of the inactive material layer on the energy density of the electrochemical device. At the same time, in the rolling process after the electrode sheet is coated, the rolling equipment acts on the inactive material layer, reducing the risk of the rolling equipment directly transitioning from the positive electrode active material layer to the positive electrode current collector, thereby causing the positive electrode segment to break.

The present application has no particular restrictions on the method for regulating the thickness of the inactive material layer, as long as the purpose of the present application can be achieved, for example, by regulating the Dv50 of the inactive material or the coating weight of the inactive material layer slurry.

In some embodiments of the present application, 0.003≤a/b≤0.025. In some embodiments of the present application, 0.003≤a/b≤0.02. For example, the value of a/b is 0.003, 0.005, 0.01, 0.015, 0.02, 0.025 or any value between any two of the above numerical ranges. When the value of a/b is regulated within the above range, the mass percentage of silicon in the positive electrode current collector and the thickness of the inactive material layer act synergistically. The thickness of the inactive material fully exerts its isolation effect without increasing the volume of the electrochemical device and affecting its energy density, isolating the electrolyte from the positive electrode current collector, reducing the possibility of the electrolyte and the positive electrode current collector reacting to produce by-products, reducing the content of by-products, and reducing the risk of by-products accumulating in specific areas or other areas of the positive electrode sheet, thereby more conducive to reducing the risk of failure of the electrochemical device during the charge and discharge cycle.

In some embodiments of the present application, 0.1≤c/b≤13. In some embodiments of the present application, 0.1≤c/b≤6.7. For example, the value of c/b is 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or any value between any two of the above numerical ranges. The inactive material layer, as an inert layer between the electrolyte and the positive electrode current collector, can physically isolate the electrolyte and regulate the value of c/b within the above range. The mass percentage of the fluorine-containing additive in the electrolyte and the thickness of the inactive material layer act synergistically, which can further reduce the possibility of the electrolyte and the positive electrode current collector reacting to produce by-products, further reduce the content of the by-products, and further reduce the risk of by-products accumulating in specific areas or other areas of the positive electrode sheet, thereby further reducing the risk of failure of the electrochemical device during the charge and discharge cycle.

In some embodiments of the present application, the fluorine-containing additive includes at least one of fluoroethylene carbonate (FEC), bis(fluoromethyl)ethylene carbonate (DFEC), bis(difluoromethyl)ethylene carbonate, bis(trifluoromethyl)ethylene carbonate, bis(2-fluoroethyl)ethylene carbonate, bis(2,2-difluoroethyl)ethylene carbonate, bis(2,2,2-trifluoroethyl)ethylene carbonate, 2-fluoroethyl methylethylene carbonate, 2,2-difluoroethyl methylethylene carbonate or 2,2,2-trifluoroethyl methylethylene carbonate. The use of the above-mentioned types of fluorine-containing additives is more conducive to reducing the oxidation ability of the positive electrode plate to the electrolyte, forming a uniform and dense protective film on the surface of the positive electrode plate and the negative electrode plate to protect the positive electrode plate and the negative electrode plate.

In some embodiments of the present application, the fluorine-containing substance includes a fluorine-containing lithium salt, and the fluorine-containing lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate (LiPF ₂ ), lithium bis(trifluoromethane)sulfonyl imide (LiTFSI), lithium bis(fluorosulfonyl imide) (LiTSI), lithium tetrafluoroborate (LiBF ₄ ), lithium difluorooxalatoborate (LiBF ₂ (C ₂ O ₄ ), LiDFOB), lithium hexafluoroantimonate (LiSbF ₆ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium perfluorobutylsulfonate (LiC ₄ F ₉ SO ₃ ), lithium bis(sulfonyl imide) (LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ )), wherein x and y are positive integers, and x≤10, y≤10) or lithium fluoride (LiF). The addition of the fluorine-containing lithium salt is more conducive to providing high ionic conductivity and making the transmission rate of lithium ions faster. Preferably, the fluorine-containing lithium salt includes at least one of LiPF ₆ , LiTFSI or LiTSI, which is more conducive to reducing the production cost of the electrochemical device. The present application has no particular limitation on the mass percentage of the fluorine-containing lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. For example, the mass percentage of the fluorine-containing lithium salt in the electrolyte is 8% to 20%.

In some embodiments of the present application, the structure of the electrode assembly is a laminate structure.

In some embodiments of the present application, as shown in FIG. 1 and FIG. 2 , the structure of the electrode assembly is a winding structure, and the positive electrode current collector 10 further includes a double-sided region 40, and the double-sided region 40 is sequentially connected to the single-sided region 30 along the winding direction W. The positive electrode active material layer 20 is disposed on both the first surface 10a and the second surface 10b of the double-sided region 40.

The present application has no particular limitation on the thickness of the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 8 μm to 20 μm.

The present application has no particular limitation on the preparation method of the positive electrode current collector, and any preparation method known in the art may be selected as long as the purpose of the present application can be achieved.

The present application has no particular limitation on the compaction density of the positive electrode sheet and the negative electrode sheet after cold pressing, as long as the purpose of the present application can be achieved. For example, the compaction density of the positive electrode sheet and the negative electrode sheet after cold pressing is 3.9 g/cm ³ to 4.3 g/cm ³ .

The positive electrode active material layer of the present application includes a positive electrode active material. The present application does not particularly limit the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include at least one of nickel cobalt manganese oxide (such as common NCM811, NCM622, NCM523, NCM111), nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO ₂ ), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate. In the present application, the positive electrode active material may also include non-metallic elements, such as fluorine, phosphorus, boron, chlorine, silicon, sulfur and other elements, which can further improve the stability of the positive electrode active material. Optionally, the positive electrode active material layer also includes a conductive agent and a binder. The present application does not particularly limit the types of conductive agents and binders in the positive electrode active material layer, as long as the purpose of the present application can be achieved. The present application does not particularly limit the mass ratio of the positive electrode active material, conductive agent and binder in the positive electrode active material layer, and those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved. For example, the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer is (97.5 to 97.9):(0.9 to 1.7):(1.0 to 2.0).

The present application has no particular limitation on the thickness of the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode active material layer is 30 μm to 120 μm.

The negative electrode sheet of the present application includes a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode active material layer arranged on at least one surface of the negative electrode current collector" means that the negative electrode active material layer can be arranged on one surface of the negative electrode current collector along its own thickness direction, or it can be arranged on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the negative electrode current collector or a partial area of the negative electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, titanium foil, foamed nickel or foamed copper, etc. The negative electrode active material layer includes negative electrode active materials. This application has no special restrictions on the type of negative electrode active materials, as long as the purpose of this application can be achieved. For example, the negative electrode active material may include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, tin-based materials, silicon-based materials, lithium titanate, transition metal nitrides or natural flake graphite. Optionally, the negative electrode active material layer also includes at least one of a conductive agent, a stabilizer, and a binder. The present application does not particularly limit the types of conductive agents, stabilizers, and binders in the negative electrode active material layer, as long as the purpose of the present application can be achieved. The present application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, stabilizer, and binder in the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the mass ratio of the negative electrode active material, conductive agent, stabilizer, and binder in the negative electrode active material layer is (97-98): (0.5-1.5): (0.5-1.5): (1.0-1.9).

The present application has no particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 5 μm to 20 μm, and the thickness of the negative electrode active material layer is 30 μm to 120 μm.

The electrolyte of the present application also includes a non-aqueous solvent. The present application has no particular restrictions on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate or propyl propionate.

The present application has no particular limitation on the mass percentage of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved. For example, the mass percentage of the non-aqueous solvent in the electrolyte is 70% to 99%.

The present application has no particular restrictions on the diaphragm and packaging bag, which may be diaphragms and packaging bags known in the art, as long as they can achieve the purpose of the present application.

The electrochemical device of the present application is not particularly limited, and may include any device that undergoes an electrochemical reaction. In some embodiments, the electrochemical device may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a sodium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The present application has no particular limitation on the preparation method of the electrochemical device, which may be any preparation method known in the art, as long as the purpose of the present application can be achieved.

The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to: a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium-ion capacitor, etc.

Example

Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods.

Test methods and equipment:

Detection of different element contents:

The lithium-ion batteries of each embodiment and comparative example were fully discharged and disassembled, the positive electrode active material layer on the surface of the positive electrode current collector was washed away with N-methylpyrrolidone, and finally the positive electrode current collector was cleaned with DMC; after cleaning, the positive electrode current collector was tested by inductively coupled plasma spectrometer (ICP) to obtain the content of aluminum and silicon elements.

Detection of fluorine-containing additives:

Take the lithium ion batteries of each embodiment and comparative example, centrifuge to obtain 10 mL of electrolyte, and use gas chromatography to obtain the mass percentage of the fluorine-containing additive in the electrolyte.

Test of average particle size Dv50:

Referring to the national standard GB/T 19077-2016 (Particle size distribution by laser diffraction method), Dv50 is measured using a laser particle size analyzer (such as Malvern Master Size 3000).

Detection of abnormality in the positive electrode:

After fully discharging the lithium-ion batteries of the embodiments and comparative examples, the positive electrode plates were disassembled and observed with the naked eye. An abnormal appearance with a different color mark (also referred to as an abnormal area) appeared, that is, there was an obvious color difference between the local area and the surrounding area. The positive electrode plates in the abnormal area were subjected to an X-ray energy spectrum analysis (EDS) test. If the silicon content in the abnormal area was >2wt%, it was determined that the positive electrode plates were abnormal. If the positive electrode plates did not have an abnormal appearance with a different color mark, it means that the positive electrode plates did not have an abnormal appearance, and the EDS test was not performed on the positive electrode plates.

The presence of an abnormal appearance of the positive electrode sheet and a silicon content >2wt% in the abnormal area are used to indicate that the electrochemical device has a failure problem during the charge and discharge cycle.

Judgment of abnormality in the manufacture of positive electrode sheets:

In the <Preparation of Positive Electrode Sheet> of each embodiment or comparative example, during the cold pressing process of the positive electrode sheet, it is determined whether the positive current collector is broken, the positive electrode sheet is broken, the positive active material layer is detached, or the laser positioning of the positive electrode sheet fluctuates greatly.

Example 1-1

The inactive material inorganic oxide aluminum oxide and the inactive material layer binder polytetrafluoroethylene (weight average molecular weight 500000) were mixed at a mass ratio of 70:30 to obtain an inactive material layer slurry, wherein the Dv50 of the inorganic oxide was 0.1 μm.

The positive electrode active material LiCoO ₂ , the conductive agent conductive carbon black, and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2:2, N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly in a vacuum mixer to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry was 70 wt %.

The positive electrode slurry is uniformly coated on the first surface 10a of the double-sided area 40 and the single-sided area 30 of the positive electrode collector 10 as shown in FIG5, and then dried at 120°C for 1 hour. The above steps are repeated on the second surface 10b of the double-sided area 40 of the positive electrode collector 10, and the inactive material layer slurry is coated on the second surface 10b of the single-sided area 30 of the positive electrode collector 10, so that the inactive material layer 50 covers the second surface 10b of the single-sided area 30, and the positive electrode sheet as shown in FIG5 is obtained. Drying treatment is carried out at 120°C for 1 hour, and then cold pressing, cutting and slitting are performed to obtain a positive electrode sheet with a specification of 78mm×875mm. Among them, the specification of the first surface 10a of the double-sided area 40 is 78mm×780mm, the specification of the first surface 10a of the single-sided area 30 is the same as the specification of the first surface 10a of the first part 31, which is 78mm×80mm, and the specification of the first empty foil area 61 is 78mm×15mm. The thickness of the positive electrode active material layer 20 is 100 μm, the thickness of the inactive material layer 50 is b μm=3 μm, and the thickness of the positive electrode current collector 10 is 10 μm. The mass percentage of silicon in the positive electrode current collector 10 is a%=0.03%.

The negative electrode active material graphite, the binder styrene butadiene rubber, and the thickener sodium carboxymethyl cellulose are mixed in a mass ratio of 97.4:1.4:1.2, deionized water is added, and the mixture is stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry, wherein the solid content of the negative electrode slurry is 75wt%. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 12μm, and then dried at 120°C for 1h to obtain a negative electrode with a coating thickness of 130μm and a single-sided negative electrode coated with a negative electrode active material layer. The above steps are repeated on the other surface of the negative electrode current collector to obtain a negative electrode sheet with a double-sided negative electrode active material layer. The negative electrode sheet is dried at 120°C for 1h, and then cold pressed, cut, and slit to obtain a negative electrode sheet with a specification of 74mm×867mm.

In an argon atmosphere glove box with a water content of <10ppm, EC, PC and DEC are mixed in a mass ratio of 1:1:1 to obtain an organic solvent, and then a fluorine-containing lithium salt LiPF ₆ is added to the organic solvent to obtain a basic electrolyte. A fluorine-containing additive FEC is added to the basic electrolyte to obtain an electrolyte. The mass percentage of the fluorine-containing lithium salt LiPF ₆ in the electrolyte is 13.8%, and the mass percentage of the fluorine-containing additive FEC in the electrolyte is c%=38%.

A porous polyethylene film with a thickness of 7 μm was used.

The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and wound to obtain an electrode assembly with a wound structure as shown in Figure 4. The electrode assembly is then placed in an aluminum-plastic film packaging bag, and after drying, the electrolyte is injected, and a lithium-ion battery is obtained through vacuum packaging, standing, formation, degassing, trimming and other processes.

Example 1-2 to Example 1-9

Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

Example 2-1 to Example 2-6

Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1.

Comparative Example 1

Except that in <Preparation of Positive Electrode Plate>, the positive electrode collector is shown as the positive electrode collector 10 in Figure 7, and the first part, that is, the second surface of the single-sided area is not provided with an inactive material layer, and the prepared positive electrode plate is as shown in Figure 7, the rest is the same as Example 1.

Comparative Example 2 to Comparative Example 3

Comparative Example 4

Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Comparative Example 1.

The relevant preparation parameters and performance tests of each embodiment and comparative example are shown in Table 1 and Table 2.

Table 1

Note: "N" in Table 1 indicates the mass ratio of inactive material and inactive material layer binder; "\" in Table 1 indicates that there is no corresponding parameter; "-" in Table 1 indicates that there is no abnormality in the positive electrode sheet and there is no need to test the Si content.

From Examples 1-1 to 1-9 and Comparative Examples 1 to 4, it can be seen that for a positive electrode current collector in which the mass percentage of silicon in the positive electrode current collector is a% within the scope of the present application, an inactive material layer is arranged on the second surface of the single-sided area of the positive electrode current collector, and a lithium ion battery with the electrolyte of the present application, after the lithium ion battery is charged and discharged, the positive electrode plate does not have an abnormal appearance, indicating that the risk of failure of the lithium ion battery during the charge and discharge cycle is reduced, and the positive electrode plate does not have a manufacturing abnormality or only has a large laser positioning fluctuation problem, which does not affect the performance of the positive electrode plate. In Comparative Examples 1 to 4, a lithium ion battery in which the second surface of the single-sided area of the positive electrode current collector is not provided with an inactive material layer, and/or the mass percentage of silicon in the positive electrode current collector is a% not within the scope of the present application, the positive electrode plate has an abnormal appearance, the Si content in the abnormal area of the positive electrode plate is greater than 2wt%, and the positive electrode plate has large laser positioning fluctuations and/or cold pressing fracture, indicating that the risk of failure of the lithium ion battery during the charge and discharge cycle has not been reduced.

Among them, the mass percentage a% of silicon in the positive current collector usually affects the risk probability of failure of the lithium-ion battery during the charge and discharge cycle. From Example 1-1 to Example 1-3, Comparative Example 2 and Comparative Example 3, it can be seen that for lithium-ion batteries with a mass percentage a% of silicon in the positive current collector within the scope of this application, the positive electrode sheet does not have an abnormal appearance, indicating that the risk of failure of the lithium-ion battery during the charge and discharge cycle is reduced, and the positive electrode sheet only has the problem of large laser positioning fluctuations, which does not affect the performance of the positive electrode sheet.

The type of inactive material usually affects the risk probability of failure of lithium-ion batteries during the charge and discharge cycle. It can be seen from Examples 1-2 and 1-4, 1-5 and 1-7 that for lithium-ion batteries with inactive materials within the scope of this application, there is no abnormal appearance of the positive electrode sheet, indicating that the risk of failure of the lithium-ion battery during the charge and discharge cycle is reduced, and there is no abnormal manufacturing of the positive electrode sheet or only a large fluctuation in laser positioning, which does not affect the performance of the positive electrode sheet. Among them, in Examples 1-5 and 1-7, when the inactive material is a non-metallic element, especially carbon (carbon is added in the form of conductive carbon), there is no large fluctuation in laser positioning during the manufacturing process of the positive electrode sheet, that is, in the continuous production process of the positive electrode sheet, after the inactive material layer is coated on the surface of the positive current collector, the laser is accurately positioned at the edge of the inactive material layer, and the coating forms a positive active material layer, thereby reducing the fluctuation of the coating starting position of the positive active material layer. In this way, the process of continuous production of the positive electrode sheet can be simplified, and the cost of manually adjusting the laser positioning of the positive active material layer can be reduced.

The Dv50 of inorganic oxides and the Dv50 of non-metallic elements usually affect the risk probability of failure of lithium-ion batteries during the charge and discharge cycle. It can be seen from Examples 1-2, 1-5 to 1-7 that for lithium-ion batteries using Dv50 of inorganic oxides and Dv50 of non-metallic elements within the scope of this application, there is no abnormal appearance of the positive electrode sheet, indicating that the risk of failure of the lithium-ion battery during the charge and discharge cycle is reduced, and there is no manufacturing abnormality of the positive electrode sheet or only a large fluctuation in laser positioning, which does not affect the performance of the positive electrode sheet.

The mass ratio of the inactive material and the inactive material layer binder usually affects the risk probability of failure of the lithium-ion battery during the charge and discharge cycle. It can be seen from Examples 1-2, 1-8 and 1-9 that for lithium-ion batteries with a mass ratio of the inactive material and the inactive material layer binder within the scope of this application, the positive electrode sheet does not have an abnormal appearance, indicating that the risk of failure of the lithium-ion battery during the charge and discharge cycle is reduced, and there is no manufacturing abnormality in the positive electrode sheet, which does not affect the performance of the positive electrode sheet.

Table 2

Note: The “-” in Table 2 means that there is no abnormality in the positive electrode and there is no need to test the Si content.

The thickness b of the inactive material layer usually affects the risk probability of failure of the lithium-ion battery during the charge and discharge cycle. It can be seen from Examples 1-2 and 2-1 to 2-2 that for lithium-ion batteries with an inactive material layer thickness b within the scope of the present application, the positive electrode sheet does not have an abnormal appearance or the positive electrode sheet has an abnormal appearance but the Si content in the abnormal area is less than 2wt%, indicating that the risk of failure of the lithium-ion battery during the charge and discharge cycle is reduced, and there is no manufacturing abnormality in the positive electrode sheet.

The value of a/b usually affects the risk probability of failure of lithium-ion batteries during the charge and discharge cycle. It can be seen from Examples 1-2, 2-1 and 2-3 that for lithium-ion batteries with a/b values within the scope of this application, the positive electrode sheet does not have an abnormal appearance or the positive electrode sheet has an abnormal appearance and the Si content in the abnormal area is less than 2wt%, indicating that the risk of failure of the lithium-ion battery during the charge and discharge cycle is reduced, and there is no manufacturing abnormality in the positive electrode sheet.

The mass percentage c% of the fluorine-containing additive in the electrolyte usually affects the risk probability of failure of the lithium-ion battery during the charge and discharge cycle. It can be seen from Examples 1-2, 2-4 and 2-5 that the lithium-ion battery with the mass percentage c% of the fluorine-containing additive in the electrolyte within the scope of the present application has no abnormal appearance of the positive electrode sheet or the positive electrode sheet has an abnormal appearance but the Si content in the abnormal area is less than 2wt%, indicating that the risk of failure of the lithium-ion battery during the charge and discharge cycle is reduced, and there is no manufacturing abnormality in the positive electrode sheet.

The type of fluorine-containing additives usually affects the risk probability of failure of lithium-ion batteries during the charge and discharge cycle. It can be seen from Examples 1-2 and 2-6 that for lithium-ion batteries using fluorine-containing additives within the scope of this application, the positive electrode sheet does not have an abnormal appearance or the positive electrode sheet has an abnormal appearance but the Si content in the abnormal area is less than 2wt%, indicating that the risk of failure of the lithium-ion battery during the charge and discharge cycle is reduced, and there is no manufacturing abnormality in the positive electrode sheet.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

An electrochemical device, comprising an electrode assembly, an electrolyte and a packaging bag containing the electrode assembly and the electrolyte, wherein the electrolyte comprises a fluorine-containing compound, the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, and the separator is disposed between the positive electrode sheet and the negative electrode sheet;

The positive electrode sheet comprises a positive electrode current collector, a positive electrode active material layer and an inactive material layer, the positive electrode current collector is an aluminum foil and comprises silicon element, and the mass percentage of the silicon element in the positive electrode current collector is a%, 0.03≤a≤0.13;

The positive electrode current collector includes a first surface and a second surface relative to each other; the positive electrode current collector has a single-sided area, the single-sided area includes a first part, the second surface of the first part is located on the outer surface of the electrode assembly, the positive electrode active material layer is arranged on the first surface of the single-sided area, and the inactive material layer is arranged on the second surface of the single-sided area; the inactive material layer includes an inactive material, and the inactive material includes at least one of an inorganic oxide or a non-metallic element.
The electrochemical device according to claim 1, wherein the inactive material layer covers the second surface of the single-sided region.
The electrochemical device according to claim 1, wherein the inorganic oxide comprises at least one of aluminum oxide, silicon oxide, calcium oxide, boehmite or calcium carbonate; and/or

The non-metallic element includes at least one of silicon, carbon or boron.
The electrochemical device according to claim 1, wherein the Dv50 of the inorganic oxide is 0.1 μm to 30 μm, and/or the Dv50 of the non-metallic element is 0.1 μm to 10 μm.
The electrochemical device according to claim 1, wherein the inactive material layer further comprises an inactive material layer binder, and the inactive material layer binder comprises at least one of polytetrafluoroethylene, chloroprene rubber, nitrile rubber, styrene-butadiene rubber, styrene-butadiene rubber, carboxyl rubber, chlorosulfonated polyethylene rubber, phenolic resin, epoxy resin or silicone resin;

The mass ratio of the inactive material to the inactive material layer binder is (70-98):(2-30).
The electrochemical device according to claim 1, wherein the fluorine-containing compound comprises a fluorine-containing additive, and the mass percentage of the fluorine-containing additive in the electrolyte is c%, and 0.1≤c≤40.0.
The electrochemical device according to claim 6, wherein the thickness of the inactive material layer is b μm, 3≤b≤20.
The electrochemical device according to claim 7, wherein 3≤b≤10.
The electrochemical device according to claim 7, wherein 0.003≤a/b≤0.025.
The electrochemical device according to claim 7, wherein 0.003≤a/b≤0.02.
The electrochemical device according to claim 7, wherein 0.1≤c/b≤13.
The electrochemical device according to claim 7, wherein 0.1≤c/b≤6.7.
The electrochemical device according to claim 6, wherein the fluorine-containing additive comprises at least one of fluoroethylene carbonate, bis(fluoromethyl)ethylene carbonate, bis(difluoromethyl)ethylene carbonate, bis(trifluoromethyl)ethylene carbonate, bis(2-fluoroethyl)ethylene carbonate, bis(2,2-difluoroethyl)ethylene carbonate, bis(2,2,2-trifluoroethyl)ethylene carbonate, 2-fluoroethyl methylethylene carbonate, 2,2-difluoroethyl methylethylene carbonate or 2,2,2-trifluoroethyl methylethylene carbonate.
The electrochemical device according to claim 1, wherein the fluorine-containing compound comprises a fluorine-containing lithium salt, and the fluorine-containing lithium salt comprises at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(trifluoromethane)sulfonyl imide, lithium bis(fluorosulfonyl imide), lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium perfluorobutylsulfonate, lithium bis(sulfonyl imide) or lithium fluoride.
The electrochemical device according to claim 1, wherein the structure of the electrode assembly is a laminate structure; or

The electrode assembly is a winding structure, and the positive electrode current collector further includes a double-sided area, and along the winding direction, the double-sided area is sequentially connected with the single-sided area.
An electronic device comprising the electrochemical device according to any one of claims 1 to 15.